1. Field of the Invention
This invention relates to telecommunications. Specifically, the present invention relates to a system and method of providing an emergency standalone switching device with a switching system interface utilized to bypass a common control and switch matrix of a digital switch.
2. Description of the Related Art
A class 5 central office comprises a building or room which houses a class 5 switching system, which operates to connect telephones and other devices used by end-user customers (“subscribers”) to a telecommunications network such as the public switched telephone network (“PSTN”). A class 5 digital switch also converts the analog signals used by telephones, modems, FAX machines, and some PBX trunks, into the digital signals that are routed through a digital telecommunications network. The class 5 digital switch also provides special services for caller ID displays and message waiting lights for subscribers, and it processes and routes calls from digital PBX trunks, ISDN lines, and digital loop carriers (“DLC”) to a telecommunications network.
U.S. patent application Ser. No. 09/998,438 (“438”) discloses a novel method and system for bypassing a common control and switch matrix of a class 5 digital switch by a switching system interface that couples one or more line/trunk frames of the digital switch to one or more transmission facilities in a communications network that preferably operates under an industry-recognized protocol.
In order to reduce the number of switches in a network, a network operator may choose to bypass the common control and switch matrix of several class 5 digital switches by placing one or more of the line/trunk frames of each of the several digital switches under the control of another digital switch that provides call processing for a larger geographical region. This may be thought of as “network flattening,” which can provide many advantages to the network operator. Specifically, lower equipment costs, lower operating and maintenance costs, more efficient use of complex software and routing databases, and simpler network management may be realized.
Although network flattening may provide some very attractive advantages, it also introduces a significant risk to network reliability by concentrating all call processing into a regional center. For example, if the transmission facility between a group of line/trunk frames and the regional center fails or is damaged, all subscribers served by the group of line/trunk frames are without telecommunications service until repairs can be made. To reduce this risk, redundant transmissions facilities may be provided that take different geographical routes to reach the regional center. However, this can be very expensive and complex to the network operator. Additional rights-of-way may need to be procured or extra transmission facilities may need to be leased. Furthermore, such “diversity routing” does not address the risk that a single regional switching center might suffer disabling damage.
It would be advantageous to have a system enabling subscribers to be able to make basic local calls, including public safety calls such as “911” calls, even if the full-featured regional center is temporarily unable to provide such call processing for any reason.
A device in the switching system interface is needed to provide minimal call processing services for basic local calls, to be used in an emergency that prevents the regional switching center from providing switching and routing services. This “emergency standalone switching” device does not need to provide the full features that subscribers expect of modern telecommunications networks, but only the ability to make basic calls in a limited area.
In addition, the switching system interface has a call control function that in normal operations routes traffic between subscriber lines terminated on legacy line/trunk frames and transmission facilities, under the call processing of a host switching system. The call control function also alerts the host system to changes in the states of subscriber lines (e.g., going off-hook), so that the host system will process call setup and call teardown.
Therefore, what is further needed is a method for the emergency standalone switching device to take over the call control function and provide call processing in the event that the host system is unable to provide call processing for any reason.
Additionally, the switching system interface has a call routing function that is controlled by the call control function and performs routing by establishing a connection between a timeslot from a line/trunk frame that represents a subscriber line and a timeslot or virtual connection in a transmission facility that connects the switching systems interface to the telecommunications network.
Therefore, a modification of the call routing function is also needed to permit a connection to be established between a pair of timeslots from one or more line/trunk frames representing a pair of subscriber lines, so that a local call can be established without the regional switching center.
Although there are no known prior art teachings of an apparatus or system such as that disclosed herein, an apparatus that discusses subject matter that bears some relation to matters discussed herein is the Lucent Technologies 5ESS® which provides an emergency standalone switching function. In particular, the 5ESS® is a remote switching unit having an emergency standalone switch which augments a fully functioning class 5 switch. However, the 5ESS® does not teach or suggest replacing or bypassing the class 5 to provide limited calling services to local subscribers.
Thus, it would be a distinct advantage to have an emergency standalone switching device in a switching system interface used to bypass the common control and switch matrix of a class 5 digital switch to provide limited calling services to local subscribers. It is an object of the present invention to provide such a system and method.